Siphonophores

colonial animals sensu stricto. Within a social insect 'colony', individuals share resources — though they aren't physically connected — and are closely related, but not genetically identical. Siphonophores are distinctive because they show the highest degree of division of labor between the individual zooids of any colonial organism. Being a siphonophore is as if you were to bud thousands of conjoined twins throughout your life, some with only legs to move everybody, others with only mouths to ingest food, others with enlarged hearts to circulate the shared blood, and others fully dedicated to the sexual production of new offspring colonies. There can be a dozen or more such functional classes of zooids in siphonophore colonies, and they are arranged in precise species-specific patterns. This pattern is usually reiterated along a linear stem, with the exact same sequence of specialized zooids occurring over and over. What's so interesting about their colonial structure? The division of labor between siphonophore zooids parallels the evolution of functional specialization at other levels of biological organization — such as between cells in a multicellular organism or between casts in eusocial insects. There is wide interest in the Siphonophores Casey Dunn What are siphonophores? Many biologists and beach-goers will be familiar with the Portuguese Man o' War, Physalia physalis, even if they may be unaware that it belongs to an extraordinary group of carnivorous colonial animals, the siphonophores. Siphonophores are members of the Cnidaria — which includes corals, sea anemones, jellyfish and hydroids. There are about 175 described siphonophore species to date. What do they look like? Unlike Physalia, most siphonophores are active swimmers that spend their entire lives in the deep-sea. They are typically elongate and rope-like, with some reaching lengths of 40 meters or more, making them the longest animals in the world — even longer than a Blue Whale. Siphonophores are gelatinous and most of them disintegrate when sampled with nets. The difficulty of collecting intact siphonophores makes the study of most species very challenging. Despite their size and abundance, we therefore know very little about even basic aspects of siphonophore biology. We do know, however, that siphonophores are unique in many respects. In particular, they have taken coloniality to an unparalleled extreme, and in so doing obtained a unique form of individuality that has led some to call them 'superorganisms'. How are siphonophores different from other colonial animals? Colonial animals consist of many …